Known to the art are drives comprising a driving pulley and a driven pulley formed by respective pairs of half-pulleys, which define respective races in which a V-shaped drive belt is wound. The axial amplitude of the race of the driving pulley is adjusted by a mechanical-control device with centrifugal action, whilst the driven pulley is normally of a reactive type, i.e., is able to adapt automatically the axial amplitude of its own race in an opposite way to what occurs for the driving pulley, to vary the diameters of winding of the belt.
In particular, for the driven pulley one of the half-pulleys is fitted in a fixed position on a drive shaft, whilst the other half-pulley is mobile towards the fixed half-pulley under the axial thrust exerted by a pre-loaded spring. The two half-pulleys are constrained together, not only by the spring but also by a device for compensating the axial thrust, which is sensitive to the torque and comprises a cam and a cam follower, which are carried by the fixed half-pulley and the mobile half-pulley, respectively, and are coupled together to provide an additional component of axial load when the drive is in the acceleration or deceleration phase.
The technique is known of making the cam and the cam follower as distinct bodies to be connected to the fixed half-pulley and, respectively, to the mobile half-pulley, for example by operations of welding or bonding.
The driven pulleys of a known type described above are in general far from satisfactory in that they are made up of a relatively large number of components and require times and hence costs for assembly that are relatively high. The drawback outlined above is basically due to the fact that the cam, the cam follower and the two half-pulleys are built using moulding processes that are separate from one another and they must be assembled together by means of a relatively large number of operations of relative positioning and connection.
EP-A-1 227 267 discloses a driven pulley having a fixed half-pulley and a mobile half-pulley as described above, wherein the fixed half-pulley in connectable to the support shaft by means of a centrifugal clutch. The driven pulley includes a device for compensating axial thrust consisting of individual cams overmoulded on a support disc that is part of the clutch and is rigidly connected to the fixed pulley, and of cam followers integral to the mobile half-pulley. To support the overmoulded cams, sheet metal inserts are provided onto the support disc.
This structure is not free form the above-referenced problems because the driven pulley is relatively complex, has a high number of pieces and entails high manufacturing costs.